When we reach for an object, for example, a cup, is the force used to hold it a reflex? Which sensorial information is used to select the force to hold it?

Why I am interested in this question

  • With the development of robots with dexterity, it is necessary to develop a minimal amount of sensors so they can choose the strength to hold an object. Objects that look heavy and slippery need more force, while objects that are delicate need a lower force. Do we unconsciously use visual information to decide the force to hold an object? Can this be called a reflex?

  • When we reach for an object and it feels painful to hold it (it is too hot or too sharp) we immediately release it, is that a reflex?

  • In my search I found mostly results about the grip reflex of newborns. Is it Completely lost in adults?

  • (a personal reason) recently, I noticed that my grip force calculation is kind of “uncalibrated”. I am dropping cups, tools, my cellphone, more frequently than before. However this is not a problem of grip Force or shaking, I can hold myself on a bar with one hand and I have zero hand shaking on my hands. So, when I consciously choose to hold it, I have force, but when I am not thinking of which force to apply, I drop things. Note: this question is not for self diagnosis, this is just the initial observation that sparked my interest in the question.

  • 3
    $\begingroup$ Seems more like a feedback loop than a reflex. That is, the grip force is adjusted depending on the weight & texture of the object. That is, when you hold an empty paper cup, a full on, a ceramic mug, or a mug used as a container for nuts & bolts, you automatically use feedback to control how much force to apply. And you can do this with your eyes closed, so visual information isn't the primary source. $\endgroup$
    – jamesqf
    Jul 19 '20 at 4:35

holding an object is usually a task that requires visual and mechanical processing (i.e. what the object looks like (i.e. what material does it seem to be made of, what is your former experience with that material, how heavy does it feel) and muscle memory.

according to the physiological definition of a reflex:

Reflex, in biology, an action consisting of comparatively simple segments of behaviour that usually occur as direct and immediate responses to particular stimuli uniquely correlated with them.

according to this same source, innate reflexes such as walking, blinking and swallowing require skeletal muscles but are still considered reflexes despite the fact that for some of these tasks (such as walking and standing) we do not know from birth (meaning reflexes can be taught and unlearned/lost).

There are other reflexes such as intestinal smooth muscle contractions etc... that we are usually completely unaware of and are controlled by the central nervous system (CNS) unconsciously.

The response to pain is also a reflex; the thermal/mechanical neural sensors in your arm (for example) send the information to your spine which directly sends a signal to your muscles to contract in order to avoid/release the object.

the palmar grasp reflex is one of many reflexes babies have that they do not need to be taught. Adults usually unteach these reflexes as some of them are not as frequently necessary in later stages of life. Newborn apes for one use the palmar grasp reflex to hold on to their mothers (it is possible that is where that reflex came from from an evolutionary standpoint).

consider that all reflexes are caused by cues that your nervous system senses and responds to. Some of these reflexes can be controlled and others not and may vary depending on your environment. A famous example of this is the pavlov's dog experiment which proved that you could also be conditioned to respond to a certain stimulus. In your case, seeing or feeling the cup is supposed to provide a stimulus to your brain reminding you that you are holding an object that requires a specific mechanical maneuver which you have learnt over time.


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